This invention relates to heat-treating furnances such as furnace systems for continuous carburizing or forging of metal parts.
Heat-treating furnace systems such as continuous carburizing plants typically include components for performing three primary processing steps: (1) a hardening step wherein the workpieces such as ferrous metal parts are heated under a controlled atmosphere (e.g. a carbon-enriched atmosphere in the case of carburizing); (2) a quench step to rapidly decrease the temperature of the parts; and (3) a reheat step wherein the parts are generally reheated to a lower temperature than employed in the hardening step in order to stress relieve the parts (e.g. tempering). In addition to these primary steps, a heat-treating system usually includes a wash unit in which residual quench media are removed from the parts prior to reheating the parts.
Furnance systems for performing these processing steps use large amounts of energy, and in conventional arrangements of furnance components considerable energy is wasted due to flue losses, wall losses, and losses in transporting parts between components. Part of the energy normally wasted in flue gas exhaust may be recovered by providing recuperators such as are shown in U.S. Pat. No. 4,113,009, "Heat Exchanger Core For Recuperator", isssued to Robert W. Meyer et al. With the exception of recuperators, however, which may be conveniently added to furnace systems as retrofit equipment, energy saving devices for heat-treating furnaces have heretofore been complex, inefficient, and difficult to integrate with existing furnaces. Yet in view of sharply escalating energy costs, furance systems which provide significant further reductions in flue losses and in the other energy looses of heat-treating equipment would be of considerable benefit to furnace technology.
Accordingly, it is an object of the present invention to provide a furnace system for heat-treating parts which is operable at high thermal efficiencies.
It is a more particular object of the invention to provide a furnace system for continuous heat-treating of parts wherein furnace components and energy transfers are arranged to maximize energy usage within the system.
It is another object to provide a thermally efficient heat-treating furnace system which is compact and occupies a relatively small amount of floor area.
It is a further object to provide an energy-efficient method for heat-treating parts.